1. Technical Field
This invention relates generally to the field of semiconductors and, more particularly, to approaches for using low resistivity metals (e.g., tungsten (W)) for forming fin-type field effect transistor (FinFET) devices such as replacement metal gate (RMG) FinFET semiconductor devices.
2. Related Art
As the semiconductor industry attempts to utilize 22 nm technology, a transition from planar complimentary metal-oxide semiconductor (CMOS) transistors to a three-dimensional (3D) FinFET device architecture has been considered. Relative to planar transistors, FinFETs offer improved channel control and, therefore, reduced short channel effects. While the gate in a planar transistor sits above the device's channel, the gate of a FinFET typically “wraps” around the channel, providing electrostatic control from both sides. Moreover, a 3D structure introduces new parasitic capacitances and new critical dimensions that must be controlled to optimize performance. Such continuous scaling of CMOS devices requires a noble metal gap fill method in RMG CMOS device fabrication.
Conventional metal gap fill in RMG CMOSFET is typically performed using aluminum (Al) metal. However, uncontrolled Al diffusion into metal gate electrodes may result in metal work function (Vt) variability, causing device performance variation. Thus, tungsten (W) is considered to be used as an alternative gap fill metal. In this case, however, a low work function (WF) (<4.4 eV) of a metal gate electrode is needed for negative channel field effect transistor (NFET) Vt tuning prior to W. As devices scale down in dimensions, the gate length (Lg) of the devices shrinks as well (e.g., down to 20 nm). As such, the resistivity of such low WF metals may be too high to be used in small gate length devices.